But with England boss Fabio Capello among the crowd at the Emirates, striker Welbeck pounced in the 81st minute to keep the champions just three points behind leaders Manchester City.

Welbeck also scored the first in the 8-2 slaughter of Arsenal at Old Trafford in August and another vital goal in the recent FA Cup third-round win at City.

But yesterday’s goal meant far more to United and their boss Sir Alex Ferguson.

The game was no classic, with some dubbing it a contest between the second-best team in north London against the second best in Manchester.

United looked fragile at times, particularly in the second half, and Wenger’s team must be rated the worst he has managed in his 16 seasons at the club.

How the Frenchman must be grateful Newcastle and Liverpool both lost on Saturday, otherwise he might have woken this morning to see his team way down in seventh, instead of clinging on to fifth.

Thierry Henry, who has a calf ­injury, might also be wondering whether his loan move was such a good idea after all.

There were boos from fans at half-time and the final whistle but the biggest show of dissent came when Wenger stunned just about everyone inside the stadium by substituting Alex Oxlade- Chamberlain in the 74th minute.

The youngster produced a ­thrilling performance on his first Premier League start and had only just set up Van Persie for the ­equaliser a few minutes earlier.

Wenger’s decision-making seemed even worse when substitute Andrey Arshavin then proceeded to play a key role in United’s winner with a shocking piece of half-hearted defending.

United had the best of the first half and went ahead through Valencia’s goal. Nani picked out Ryan Giggs on the overlap and his cross was so inviting for the Ecuadorian, who evaded Thomas Vermaelen to bury a fine header.

At half-time, Wenger replaced Johan Djourou with 18-year-old Nico Yennaris after the centre-back put in an abysmal ­display at right-back.

Next came Van Persie’s moment of misery. After Chris Smalling slipped Tomas Rosicky nipped in and raced into the box.

He passed to the Dutchman, who drifted away from Jonny Evans but, with the goal gaping, smashed wide from eight yards.

Welbeck came close to scoring in the 64th minute, slipping the ball past Wojciech Szczesny, but Per Mertesacker slid in to clear.

Arsenal’s equaliser came from a fine move. Laurent Koscielny ­tackled Rafael superbly in the box and broke out to pass to Rosicky.

He moved the ball on to Oxlade-Chamberlain, who picked out Van Persie’s diagonal run.

The Arsenal skipper turned and shot, with the ball going through Evans’ legs and in off the far post for his 19th league goal of the season.

Amazingly, Wenger then opted to replaced Oxlade-Chamberlain.

That decision turned out to be disastrous when replacement Arshavin was beaten with ease by Valencia, who played a snappy one-two with Ji-Sung Park and then teed up Welbeck to smash home.

Wenger looked furious, beating the ground in frustration. Really, he should have been beating ­himself up.

United’s Phil Jones was last night ruled out for at least two weeks with ankle ligament damage.